Distributed computer environments, such as computer networks, provide significant advantages to multiple computer clients or users. In particular, distributed environments allow multiple clients to actually share many different computer resources including both hardware and software resources. Sharing software-related resources provides many known benefits, such as the fact that only one such resource needs to be created, updated and maintained.
The Internet is one particular example of a distributed environment that provides access to a considerable number of software resources, which are available to practically any client computer system having Internet capabilities. One portion of the Internet is known as the World Wide Web which is a generally a system of Internet servers that house software related resources that are formatted in a particular manner, such as with HTML (HyperText Markup Language). The protocol for accessing these particular resources is known as the HyperText Transfer Protocol or HTTP. It should be noted however that not all Internet servers are part of the World Wide Web.
Historically, most resources on the Internet corresponded to web page files that included only static HTML code, and thus were only available for display. However, recent advances are being made in the representative functionality provided to client systems to provide more interaction between the client and server systems. For instance, clients may effectively author resources on a server system from client systems over distributed networks, including the Internet. Indeed, much time and effort has been spent on the development of a WebDAV protocol or standard, which stands for the World Wide Web Distributed Authoring and Versioning standard, referred to herein as simply “DAV.” DAV provides a set of headers and methods which extend HTTP to provide capabilities for managing properties, namespace and other items from a client system in order to allow client computer systems to access server-side resources for the purpose of editing those resources. Proposed Standard RFC 2518, which is a document written by the IETF and approved by the IESG, published February 1999, describes DAV in more detail.
As part of the DAV standard, server computer systems provide various services in managing the various access requests made by clients. One particular service relates to controlling when a resource is available for use by a client. That is, DAV provides methods that allow a client to lock a resource when using that resource so that subsequent users may not access that resource during that time. This locking scheme helps prevent the “lost update” problem associated with two or more users modifying a resource simultaneously such that editions are inadvertently lost. Unfortunately however, the DAV protocol only provides two types of locks, an exclusive write lock and a shared write lock.
Although the exclusive and shared write locks are helpful in preventing the lost update problem, DAV does not support open sharing modes found in existing platforms, such as the Win32® platform. For example, if a client is not concerned with whether others edit or delete a resource it is using, but wants to prevent others from reading that resource while it is being used, the Win32® platform supports such a lock, but there is no method to support this lock function in DAV. Similarly, if a user wants to prevent others from deleting a resource, but is not concerned with whether others read a resource, the Win32® platform supports this function but there is no method to support this function in DAV.
The inability to provide these types of sharing procedures raises significant compatibility issues since many existing applications, such as word processing applications, utilize these open sharing modes. Consequently, when those applications are used over the Internet in combination with the DAV protocol, the open sharing modes are not supported. Therefore, much of the functionality is not available and may even cause errors to occur when attempting to use these unsupported methods.
Another drawback associated with the limited locking scheme relates to the fact that the locks are mandatory in the DAV protocol. That is, the DAV protocol cannot express advisory locks, which are well known in the UNIX platform. In the UNIX platform, cooperating applications can check for the presence of advisory locks that conflict with the attempted operation and honor that advisory lock, but there is no requirement to honor the lock. An application is therefore allowed to access a resource and edit that resource even when such access conflicts with an advisory lock. Although this scheme is prevalent in UNIX applications, there is no mechanism in DAV to create a lock that is advisory. Consequently, many Unix applications are incompatible with the DAV protocol.
It is with respect to these and other considerations that the present invention has been made.